The ideal solution for achieving utmost insulation against heat transfer and sound transmission consists in using a double-wall vacuum-tight casing, in which a high vacuum of less than 0.1 pascal, that is less than 10.sup.-3 torr, can be created and maintained for a very long period. It is known that the heat transfer factor across a double-wall casing of this kind is very close to zero, while its acoustic transmission factor is practically nil.
However, this solution which is well known and is used for the storage and shipping of cryogenic liquids, and also for carrying around hot or refrigerated beverages in containers known as "Thermos" vessels, implies a relatively heavy and costly structure, when it is made of metal, or a fragile structure when glass is used. Also, such a structure runs the risk of loosing all its useful properties through a single puncture or fissure.
It has therefore already been proposed to produce a casing of this kind by incorporating, between panels of alveolar material, hollow tubular elements inside which a high vacuum has been created. Insulating panels of this type have been described in French Pat. No. 1,284,186 of Johns-Manville and No. 1,255,980 of Yuen, and in the German Pat. No. 2,629,171 of Rodrian. However, in these three earlier patents, the vacuum tubes or enclosures are either metallic or made of glass, and when plastic tubes are mentioned, no means are indicated for achieving an easy and effective sealing of these tubes, nor for ensuring their vacuum tightness in the course of time.
As regards freezing tunnels, cold-storage cabinets and sound-proofing enclosures, which have been mentioned hereinabove, these devices are usually insulated by means of mats of glass fibers or panels of alveolar material which generally fail to prevent a substantial transmission of heat.
Similarly, the problem of providing protection against intense solar radiation striking upon the metal structure of the roof of an automobile, of a caravan or a truck being used in a hot country, had not yet been satisfactorily solved. Also, similar problems arise when dealing with the soundproofing of cabins for listening to music, or of rooms which require to be protected against external noise. A further similar problem relates to soundproof enclosures which are increasingly being required in the case of very noisy machines, such as paperboard corrugating machines, etc.
It is a purpose of this invention to achieve tubular vacuum-tight enclosures having a high thermal and acoustic insulating power for bringing a better solution to the above-mentioned problems.